Techniques for charging or discharging a capacitor include open-loop switches and various types of linear buffers. A simple series circuit composed of a voltage source, switch and capacitor will cause the capacitor to charge when the switch is closed. An open-loop switch diverts current from more useful parts of the circuit. Further, an open-loop switch is limited by the source impedance of the voltage reference node in combination with the impedance of the switch itself. For particularly large values of resistance and/or capacitance, an open-loop switch charge/discharge system can have an RC time constant which may be too long. Connecting a simple switch between the two nodes is limited to configurations where the RC delay created by the reference source impedance in combination with the capacitor's impedance is small, and where it is acceptable to draw current from the reference node.
Using a linear buffer to drive a capacitor to a particular voltage eliminates an overshoot error, however, an error due to offset in the buffer still exists. Linear buffers require a power output stage or large quiescent current for applications requiring charging a large capacitor quickly. For linear buffers using more than one gain stage it is difficult to compensate for a large range of output capacitor values. A linear buffer with high quiescent current is typically unacceptable in a circuit functioning only during error conditions. Further, a linear buffer is not suitable for operation near the supply rail voltages, because most buffers lose gain near the supply rails.